the idle speed control valve is underneath the throttle body bolted to the manifold, bit of a pig to get to. best off going from underneath with an 8mm (i think) spanner.

it works the same as ya corsa ie spring, you can clean it but it wont last too long, best off getting a new one.

if that dopesnt solve the problem, check the PCV valve on the front. underneath the manifold, if that is leaking it will cause rough idling too